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• o Collection of quarterly water quality samples <br />at the inlet structure of the culvert beneath <br />the fill after completion; <br />o Flow measurement at the culvert after <br />installation. This measurement should be <br />taken monthly and during major flow events. <br />2.6 Proposed Hydraulic Structures <br />Three types of hydraulic and sediment control structures are <br />proposed for the portal area. A culvert is required to pass <br />flows in East Roatcap Creek under the portal bench and haul road. <br />A diversion ditch is proposed to intercept flows from the west <br />hill slope before these flows enter the disturbed portal area, <br />and a sediment pond is required to intercept runoff from the <br />portal bench and cut slopes. <br />Additional sediment control measures are proposed for use on <br />the fill slopes. These measures will consist of surface <br />protection measures such as revegetation and mulching, and <br />detention and filtering structures such as filter fences, <br />detention structures with rock outlets, straw bales or other <br />sediment filtering measures. <br />These hydraulic and sediment control measures have been <br />evaluated at the reconnaissance level. This evaluation and <br />recommendations for final design are described below. <br />2.7 East Roatcap Creek Culvert <br />2.7.1 General Description <br />The East Roatcap Creek Culvert is required to pass flows <br />from the East Roatcap Creek Watershed through the portal bench <br />and haul road fill. Flow rates for runoff resulting from <br />rainfall having various recurrence intervals have been calculated <br />and are shown in Table H-1 of this report. Flows resulting from <br />three recurrence interval storm events have been selected for use <br />in the design of this culvert: <br />410 - 56.9 cfs; <br />4100 - 95.0 cfs; <br />4500 - 123 cfs. <br />2.7.2 Design Criteria <br />The State of Colorado Mined Land Reclamation Division <br />Regulations require culverts with an end area of less than 35 <br />square feet to safely pass the runoff a 10-year, 24-hour <br />6 <br />